1. Field of the Invention
The present invention relates to a method and apparatus for recording and reproducing image data, particularly electronic watermark information embedded (hidden) in video signals, which is used for the picture recording and reproduction control or for marking the origins of the records, and also relates to a recording medium on which electronic watermark information is recorded by being embedded in a video signal.
2. Description of the Prior Art
Among the several schemes proposed for embedding electronic watermark information in video signals, representative one is described in the article entitled xe2x80x9cData Hiding Techniquexe2x80x9d in publication ITE Technical Report, Vol.21, No.31, pp.3-8. Another conventional information embedding technique is described in publication Nikkei Electronics, No.683, pp.99-107, published in 1997. These conventional techniques are intended to embed, in a video signal, information that is different in terms of statistical characteristics of image from the inherent picture information carried by the video signal, and use the embedded information at the time of picture reproduction for identifying the origin of the record or producing a control signal which enables or disable the reproducing of the video signal.
However, these publications mainly describe recording means and do not describe the details of means of detecting electronic watermark information at the time of reproducing. Electronic watermark information recorded by a VCR or optical disk unit has its reproduced signal level varied depending on the reproduction characteristics of these apparatus. The reproduced signal waveform of the electronic watermark information varies also depending on the frequency characteristics of these apparatus.
An object of the present invention is to provide a method and apparatus for recording and reproducing electronic watermark information and a recording medium which enable easy detection of the watermark information at the time of reproducing.
Another object of the present invention is to provide a method and apparatus for recording and reproducing electronic watermark information and a recording medium which enable easy reproduction of the embedded electronic watermark information even if the reproduction characteristics of the reproduction apparatus vary.
Still another object of the present invention is to provide a method and apparatus for recording and reproducing electronic watermark information and a recording medium which enable easy reproduction of the electronic watermark information even if the signal level of the watermark information varies.
Still another object of the present invention is to provide a circuit arrangement which is scarcely affected by the reproduction level and frequency characteristics of the recording apparatus in detecting electronic watermark information included in a video signal which has been recorded by the recording apparatus.
In order to achieve the above objectives, the recording medium based on this invention is designed to record a video signal, electronic watermark information which is embedded in the video signal and a reference signal which is inserted at a position different from the position of the watermark information in the video signal.
The inventive method of recording electronic watermark information includes the operational steps of embedding electronic watermark information in a video signal at a minimal disturbance against the video signal, and recording a reference signal which is inserted at a position different from the position of the watermark information in the video signal.
The inventive method of recording and reproducing electronic watermark information includes the operational steps of recording electronic watermark information which is embedded in a video signal at a minimal disturbance against the video signal and a reference signal which is inserted at a position different from the position of the watermark information, reproducing the reference signal, and modifying the watermark information based on the reference signal.
The inventive method of recording electronic watermark information includes the operational steps of calculating the visually-permissible alteration range of luminous value of the luminance signal included in a video signal, and altering the luminous value of the luminance signal at a predetermined position within the calculated alteration range.
The inventive method of recording electronic watermark information includes the operational steps of calculating the visually-permissible alteration range of luminous value of the luminance signal included in a video signal, and altering the luminous value of the luminance signal at a predetermined position in case the altered luminous value is within the calculated alteration range.
The inventive method of reproducing electronic watermark information includes the operational steps of detecting a reference signal for detecting electronic watermark information from a recording medium on which are recorded a video signal, the watermark information which is embedded in the video signal at a minimal disturbance against the video signal and the reference signal which is inserted at a position different from the position of the watermark information, and modifying the watermark information based on the reference signal.
The inventive method of reproducing electronic watermark information includes the operational steps of detecting a reference signal for reproducing electronic watermark information from a recording medium on which are recorded a video signal, the watermark information which is embedded in the video signal based on the alteration of luminous value of the luminance signal included in the video signal and the reference signal which is inserted at a position different from the position of the watermark information, and modifying the luminous value of the watermark information based on the reference signal.
The inventive method of recording and reproducing electronic watermark information includes the operational steps of recording a video signal, electronic watermark information which is embedded in the video signal at a minimal disturbance against the video signal and a reference signal which is inserted at a position different from the position of the watermark information, and detecting the watermark information based on the reference signal.
The inventive method of recording electronic watermark information includes the operational steps of recording a video signal, electronic watermark information which is embedded in the video signal at a minimal disturbance against the video signal and a reference signal which is inserted at a position different from the position of the watermark information.
The inventive method of reproducing electronic watermark information includes the operational steps of detecting electronic watermark information based on a reference signal thereby to reproduce the watermark information from a recording medium on which are recorded a video signal, the watermark information which is embedded in the video signal at a minimal disturbance against the video signal and the reference signal which is inserted at a position different from the position of the watermark information.
The inventive apparatus for recording electronic watermark information comprises a detection circuit which calculates the permissible alteration range of luminous value depending on the luminous value of the luminance signal included in a video signal, and a watermark information embedment processing circuit which embeds electronic watermark information in the video signal by altering the luminous value of the luminance signal at a predetermined position within the calculated alteration range.
The inventive apparatus for recording electronic watermark information comprises a detection circuit which calculates the permissible alteration range of luminous value depending on the luminous value of the luminance signal included in a video signal, and a watermark information embedment processing circuit which embeds electronic watermark information in the video signal by altering the luminous value of the luminance signal at a predetermined position in case the altered luminous value is within the calculated alteration range.
The inventive apparatus for reproducing electronic watermark information comprises a detection means for detecting electronic watermark information based on a reference signal thereby to reproduce the watermark information from a recording medium on which are recorded a video signal, the watermark information which is embedded at a minimal disturbance against the video signal and the reference signal which is inserted at a position different from the position of the watermark information.
In the inventive electronic watermark information reproducing apparatus, the detection means includes a detection signal generating circuit which generates a detection signal for detecting a reference signal from a sync signal, a sample-holding circuit which samples and holds the amplitude of the reference signal in response to the detection signal, a gain drift calculating circuit which calculates the gain drift based on the amplitude of the reference signal provided by the sample-holding circuit, a modification circuit which modifies the luminance signal included in the video signal based on the calculation result provided by the gain drift calculating circuit, and a watermark information detecting circuit which detects the watermark information from the modified luminance signal by using the detection signal.
In the inventive electronic watermark information reproducing apparatus, the detection means includes a detection signal generating circuit which generates a detection signal for detecting a reference signal from a sync signal, a sample-holding circuit which samples and holds the amplitude of the reference signal in response to the detection signal, a gain drift calculating circuit which calculates the gain drift based on the amplitude of the reference signal provided by the sample-holding circuit, a detection circuit which detects the watermark information from the luminance signal included in the video signal by using the detection signal, and a modification circuit which modifies the amplitude of the detected watermark information based on the gain drift calculated by the gain drift calculating circuit.
The inventive apparatus for reproducing electronic watermark information comprises a watermark information detecting circuit which detects an electronic watermark signal from a video signal, a reference signal detecting circuit which detects a reference signal, and a modification circuit which modifies the amplitude of the watermark signal in response to the drop in amplitude of the reference signal.
In the electronic watermark information reproduction apparatus, the modification circuit includes a gain drift calculating circuit which calculates the drop of gain of the reference signal.
In the electronic watermark information reproduction apparatus, the watermark information detecting circuit includes an information position generating circuit which generates a watermark information position detection signal based on the sync signal.
In the electronic watermark information reproduction apparatus, the reference signal detection circuit includes a reference signal position detecting circuit which generates a reference signal position detection signal based on a sync signal.
The inventive method and apparatus are designed to append preparatorily a reference signal used for the detection of electronic watermark information at a specific position of a video signal and reproduce the watermark information based on this reference signal at the time of reproducing. The reference signal is embedded within the period of horizontal sync signal outside the picture display period, i.e., in the back-porch or front-porch portion, or outside the picture display area. At the time of detection, the embedded electronic watermark information is reproduced based on the reference signal level.
Alternatively, the reference signal may be recorded within the period of vertical sync signal. A reference timing signal is recorded at the head of the video signal so that the recording level and recording position of the electronic watermark information are detected based on the reference signal level and reproduction timing at the time of reproducing.